Generally, there are many types of vehicle keys, such as a plate-shaped basic key inserted directly into a key box by a user to start an engine, a remote control key having the functions of opening/closing the doors of the vehicle and starting an engine from a remote distance embedded therein, and a smart key capable of releasing a door locking state if a driver approaches the vehicle in a state of being carried with him and starting an engine by means of pressing a button after he gets in the vehicle.
Further, there has been recently suggested a portable device that transmits an ID code signal inclusive of an ID code so as to conduct vehicle immobilization.
If a user gets in the vehicle with such portable device carried by him, the ID code signal of the portable device is automatically transmitted to an ECU of the vehicle to check whether the ID code of the portable device corresponds with a previously set ID code in the ECU. If it corresponds therewith, an ignition switch (button) is pressed to activate a start motor, thereby making the engine of the vehicle started.
By the way, if the ID code signal is not automatically transmitted to the ECU of the vehicle because of the voltage drop of the battery of the portable device, the portable device is inserted into a portable device holder mounted in the vehicle, so that a coil antenna (immobilizer coil) mounted in the portable device holder transmits driving waves to a transponder in the portable device and thus generates an electromotive force capable of transmitting the ID code signal to the ECU of the vehicle again, thereby making the engine started.
In the above-mentioned conventional practices, however, the portable device holder for mounting the coil antenna from which driving waves are transmitted to the portable device to generate the electromotive force from the portable device should be mounted in the interior of the vehicle, thereby undesirably increasing manufacturing costs and manufacturing processes for the portable device holder and making the space in the vehicle in which components having other functions are provided reduced because of the space occupied by the portable device holder.